Erectile dysfunction (ED) is a common complication after radical prostatectomy (RP) for prostate cancer and is due to the injury of the cavernosal nerve during surgery. Despite the improvement of the nerve sparing technique, still many men develop ED after surgery. Until these surgical techniques are perfected to the point where this can be performed without any temporary or permanent injury to the nerves, it seems logical to focus on the prevention of the detrimental and irreversible changes that befall the corporal tissue as a result of the neural injury. We postulate that this process can be studied in rats subjected to bilateral cavernosal nerve resection (BCNR) which is the most severe form of injury that can occur to the nerves, or the bilateral nerve crush model (BCNC) which is a less severe form of neural injury since there is no transection of the axon, and in transgenic mice, to investigate these hypotheses: (1) the corporal fibrosis and smooth muscle cell (SMC) apoptosis induced by BCNR/BCNC can be prevented pharmacologically by the continuous and long-term administration of either PDE5 inhibitors, which increases intracorporeal NO and cGMP. Such treatment leads to a reduction in collagen deposition (decrease in fibrosis) and a positive SM turnover (increase in SMC number) as a result of a reduction in the increased oxidative stress and TGF-beta levels induced by the neural injury. (2) The neural injury induced by BCNR/BCNC may be ameliorated by the modulation of NO/cGMP pathway;through the activation of Pi3K-Akt pathway, inducing neurogenesis, leading to partial axonal regeneration and improvement of the erectile response. To test these hypotheses we propose: Aim 1: To determine the relative effects of modulating the NO and cGMP pathway on corporal collagen and SM turnover rates oxidative stress, neuronal, and smooth muscle apoptosis after BCNR. Aim 2: To determine the mechanism by which NO and/or cGMP preserves the corporal SMC and to ascertain the roles of PKG (protein kinase G) or PKA (protein kinase A) in this process. Aim 3: To determine whether the stimulation of the NO/cGMP pathway induces the release of neurotrophic factors that may lead to regeneration of cavernosal nerves via the Pi3K-AKT pathway. Endpoints: (a) functional determinations of erectile response like electrical field stimulation and cavernosometry;(b) immunohistochemistry for markers of fibrosis, oxidative stress, nitrosative reaction, collagen, SMC turnover, nerve regeneration, and neurotrophic factors;(c) Western blot analysis for some of these markers;(d) assays with selective NO/cGMP modulators in cell culture.